Heat cured binders based upon furan resins and furfuryl alcohol are well known. See for example U.S. Pat. Nos. 4,317,763, 4,451,577, and 4,383,098 which describe heat cured foundry binders, typically cured in the presence of a latent acid curing catalyst. These binders are preferred for some applications because of their price, the availability of equipment, and the dimensional accuracy of the foundry shapes made with them.
Typically heat cured binders, particularly hot-box binders, which are cured at temperatures of 100.degree. C. to 300.degree. C. in the presence of a latent acid curing catalyst, contain urea and other nitrogen containing compounds which scavenge free formaldehyde and provide extra strength to foundry shapes made with such binders. A problem with these heat curable foundry binders is that their high nitrogen content causes casting defects during metal casting processes such as pinholing and porosity. Another problem is that these binders contain free formaldehyde which is to be avoided.
It is also known that the bench life of foundry mixes made with these binders is often inadequate due to the presence of the latent acid-curing catalyst in the foundry mix. The bench life of the foundry mix is the time period between forming the mixture of the aggregate and binder and the time when the mixture is no longer useful for making acceptable molds and cores. A measure of mold and core acceptability is tensile strength. If a foundry mix consisting of aggregate and binder composition is used after the bench life has expired, the resulting molds and cores will have insufficient tensile strength.
Since the foundry mix made with a heat curable binder contains a latent acid curing catalyst in addition to the aggregate and resin, the catalyst and resin may react prior to shaping the mix into foundry molds and cores. If this reaction occurs, it will reduce the flowability of the foundry mix and the resulting molds and cores will have reduced strength. Additionally, it will be necessary to clean the hoppers, in which the foundry mix is stored, more frequently. This is time consuming and expensive.